Molded articles made from thermoplastic resin foamed materials of, e.g., polystyrene, polyethylene, or polypropylene, such as insulating containers for fishes and fruits, cushioning materials (e.g., corner pad) for appliances, trays for foods and fruits, and cups for drinks, are used today in huge quantities, and the use is extending steadily.
Since these molded articles made from thermoplastic resin foamed materials after use are not spontaneously rotten or degraded, extensive efforts have been made to make effective use of them as a recycle thereby to prevent them from causing environmental pollution. For example, they can be burnt to utilize a generated heat energy or can be heat melted to obtain reprocessed plastics. Further, molded articles after use are ground for use as a draining cobblestones to be spread on the bottom of a flowerpot or as a soil conditioner to be incorporated into clayey soils.
A soil mixed with grinds of thermoplastic resin foamed materials, on one hand, has improved properties necessary for growth of roots, i.e., air permeability, hydrophobic properties, and heat retaining properties, but, on the other hand, is poor in water retention and fertilizer retention that are also necessary for growth of plants. Moreover, because the grinds of foamed materials are extremely lighter than general soils, they float off the soil for every rainfall or sprinkling. Further, draining cobblestones made from foamed materials are crushed beneath the soil during long-term use due to low compressive strength and reduce their volume. As a result, drainage is deteriorated, or the cobblestones are carried away from drainage holes.
In order to overcome these disadvantages, a soil conditioner comprising foamed polystyrene ground particles having adhered thereonto a sand or a powdered fertilizer, e.g., cow dung, with an organic solvent, an adhesive, etc. has been proposed as disclosed in JP-B-57-61064 (the term "JP-B" as used herein means an "examined published Japanese patent application") and JP-B-U-61-2651 (the term "JP-B-U" as used herein means an "examined published Japanese utility model application"). However, not only expensiveness of the organic solvent or adhesive but the problem of solvent recovery have been bars to putting such a soil conditioner to practical use. Further, JP-A-49-40321 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a process for producing an artificial granular soil from foamed polystyrene, in which a large quantity of an inorganic powder and a large quantity of foamed polystyrene particles are mixed and stirred together with an adhesive or a pulp waste liquor as a binder, once granulating the mixture, and heating the granules to fuse the foamed particles to obtain porous particulate lumps. However, the process is not deemed efficient because granulation using a binder and heat fusion of foamed polystyrene particles must be separately carried out.